In a known manner, such crediting means are used as means for allowing access; a known example of this is a bank credit card which allows money to be withdrawn from some distributor terminal units in addition to payment to other specific terminal units. In the example mentioned hereinabove it is conventional to leave some terminal units practically without any supervision by banks which own centralized processing machines for transactions and also not to supervise the bearers of crediting means.
As such means are intended to keep the accesses which they control exclusively for authorized users, it is to be feared that malevolent third parties will attempt to take fraudulent advantage of the possibilities afforded by passing themselves off as authorized users or by falsifying the data.
This leads to checking the identity of the bearers of crediting means via terminals by comparing the confidential digital data registered on the crediting means with confidential data composed by bearers. However, it may be feared that such confidential data will possibly become known at the terminal units and be used to modify or add data.
Likewise, data transmitted by links over long distances is coded to prevent fraudulent tapping of confidential data by connecting a tap line to the links and hence the transmission of false data. Now, in the case of communications between two parties via a third party, said third party is particularly well placed to modify data exchanged by the other two to his benefit.
To remedy these drawbacks, the invention proposes a method and devices which tend to prevent the communication of the private data of each of the parties and to approve the data emitted.